In recent years, from the point of view of reducing carbon dioxide emissions and increasing energy utilization efficiency, electric vehicles using electricity as a power source have been put into practical use. Accordingly, charging infrastructure for electric vehicles has been started to be built in various places. In order to fully charge a battery for a common electric vehicle, electricity amount of as much as 10 kWh (amount for two or three days in terms of an average power consumption of an average family) is needed. For this reason, in the field of an electric power supply facility (grid) for electric vehicles, it is an issue to enhance functions such as a load control function and distribution control function, and the next-generation power network called a “smart grid” embedded with a means for automatically controlling demand and supply of electric power is gathering attention. In the field of a power network managed by a smart grid, a demand forecast of charging (power supply from the grid to the vehicle) of an on-board battery and a charging control based on the forecast are taken into consideration.
As electric vehicles spread, it is becoming common practice to install in a household a charging equipment capable of charging an on-board battery. As a charging equipment, examples include outdoor outlets, circuit breakers, distribution boards, and the like dedicated for charging a battery. In these charging equipments, the maximum value of a chargeable electric current value is extended to 30 A or higher in accordance with a charging specification of an electric vehicle (the maximum value is approximately 15 A in the case of existing home circuit breakers).
On the other hand, the charging specification (the maximum value, the minimum value, and the like of a chargeable current and voltage) of an electric vehicle depends on types of vehicles, and the value of the electric current flowing through the charging cable when charging the battery is determined on the side of the charging device on the vehicle; thus, it is difficult for one charging equipment to satisfy charging specifications of various electric vehicles. In addition, the fact that the specification (including a value of a current flowing through a circuit breaker installed in a household) of the charging equipment is limited by regulations that vary according to nations and local governments makes the issue more difficult.
To solve this issue, a technique is proposed in which the charging equipment informs the electric vehicle of the value of a suppliable electric current. The techniques include, for example, communication using a control pilot signal defined in IEC61851 (hereinafter, referred to as a “control pilot communication”) and communication using the communication protocol developed by CHAdeMO Association (“CHAdeMO” is a proprietary name). In these techniques, in the charging cable connecting the electric vehicle and the charging equipment, there is provided a signal line (communication line) for communication in addition to the power line for charging the battery, and the communication is performed between the charging equipment and the electric vehicle through the signal line.
The control pilot communication provides an arrangement in which a signal line voltage and a duty ratio of a PWM (Pulse Width Modulation) signal are used to inform not only connection/disconnection of the charging cable but the value of the suppliable electric current from the charging equipment to the electric vehicle. The communication protocol developed by the CHAdeMO Association (“CHAdeMO” is a proprietary name) provides an arrangement in which CAN (Controller Area Network) communication is used not only to inform the electric vehicle of the value of the electric current suppliable from the charging equipment but to inform the charging equipment of an upper limit (withstand voltage) of a voltage chargeable from the electric vehicle, a filling rate of the battery, and the like.
However, the control pilot communication and CAN communication have limitations in a communication speed and a volume of data to be transmitted at a time (for example, CAN communication can transmit only 8 bytes of data at a time). Thus, it is difficult to realize a use case considered for the smart grid (for example, the communication of billing information between the electric vehicle and the charging equipment, and the provision of a power generation schedule from the system side to the electric vehicle).
To address this issue, in recent years, it is being studied that PLC (Power Line Communication) communication as disclosed in Patent Document 1 is performed on the power line of the charging cable to perform the communication between the charging equipment and the electric vehicle. PLC communication realizes communication on the commercial alternating-current power line of 100 V (volt) or 200 V, and can transmit and receive a greater amount of data than the control pilot communication and CAN communication.
However, the power line which serves as a communication path for PLC communication is branched on a switchboard in a household and is connected to other appliances such as an air conditioner and a refrigerator. Thus, noise created by an inverter in an air conditioner in a house, for example, can reach the charging cable connected to the charging equipment in the same house. If the noise reaches the charging cable, the PLC communication using the charging cable cannot be normally performed. Also, the power line in the house is connected to a neighboring house through the outdoor power line. Thus, in the PLC communication, for example, there may a problem of communication leak that a charging equipment in a house erroneously communicates with an electric vehicle connected to a charging equipment in a neighboring house, and there may be a problem of leakage electric field, from an outdoor power line, caused by communication.
As a result, when configuring a system performing PLC communication between the electric vehicle and the charging equipment, a wiring plan of power lines is needed to be made, taking a leakage of communication and a leakage electric field into account.